This invention relates to a mobile telephone device having steal prevention function. Such a mobile telephone device is particularly useful in a portable radio telephone device.
An example of the mobile telephone device is disclosed in Japanese Patent Publication No. Tokkosho 63-65250 (65250/1988). The mobile telephone device is used in a steal prevention system. The steal prevention system is for the mobile telephone device which is used on an automobile and aims to carry out a follow-up survey when the automobile having the mobile telephone device was stolen. Namely, the steal prevention system is for establishing the follow-up survey of a stolen automobile even if the mobile telephone device loaded on the stolen automobile is not used. The steal prevention system is based on the fact that the mobile telephone device has a preassigned call number. In the following description, the mobile telephone device loaded on the stolen automobile is called a stolen mobile telephone device.
In order to establish the above-mentioned purpose, the steal prevention system comprises a base station for connecting the mobile telephone device to a telephone network. The steal prevention system is on the premise that a call number of the stolen mobile telephone device is registered, as a stolen call number, in the base station. For the reason, the base station comprises a memory unit memorizing the stolen call number. The base station transmits an information signal including the stolen call number.
On the other hand, the mobile telephone device receives the information signal even if the mobile telephone device is not used, namely, even if a power switch is put into an off state. The mobile telephone device comprises a power supply unit which is removably attached to a body of the mobile telephone device and a decision section for carrying out a decision operation whether or not the preassigned call number coincides with the stolen call number included in the information signal. When the decision section decides that the preassigned call number coincides with the stolen call number, a transmitting section is activated and transmits an alarm signal representative of a fact that the preassigned call number coincides with the stolen call number.
When the alarm signal is received by the base station, the alarm signal is displayed by a display unit in the base station. Then, the base station carries out the follow-up survey of the stolen automobile by the use of the alarm signal.
As mentioned above, since the mobile telephone device always monitors the information signal, the mobile telephone device has an increased power consumption. This means that the increased power consumption hastens voltage drop of the power supply unit.
Furthermore, if the power supply unit is removed from the body of the mobile telephone device, it is impossible to monitor the information signal and to transmit the alarm signal. This means that it is impossible to establish the above-mentioned purpose. The above-mentioned operation is applied to the mobile telephone device which is not loaded on the automobile.